The present invention relates to a bioreactor for growing cell culture.
Cell culture has greatly increased in recent years due to two advances: (1) micro carriers and (2) hybridomas.
Mammalian cells can be classified as being either anchorage dependant or suspension cells. Normal cells (as distinct from cancer cells) are "anchorage dependent"; they need a hydrophilic solid surface to attach themselves to, before they will propagate themselves by division. They are grown on the inside of horizontal cylindrical glass roller bottles; this is a tedious batch operation unsuitable for mass production. However, by growing anchorage dependent cells on minute solid particles ("micro carriers") kept in suspension in a stirred vessel, large scale production becomes possible. Hybridoma cells are hybrids produced by fusing myelona (cancer cells) with cells which express monoclonal antibodies; these hydrids are not anchorage dependent and do not require micro carriers to keep them in suspension.
Both types of cells require gentle stirring. The initial stage of "plating" normal cells on micro carriers is especially critical. Both types of cells require a liquid medium containing nutrients and dissolved oxygen and carbon dioxide. In the past these gases have been supplied from the head space above the liquid medium which half fills a flask. But such a method of oxygenation becomes insufficient when the volume of the liquid medium is greater than about 3 liters.
The problem of oxygenation has become a critical one. Several methods of overcoming this difficulty have been used:
(1) "Sparging" which is the introduction of gases through a sparger at the bottom of the flask; PA1 (2) Introduction of gas through a permeable membrane or tube (immersed in the medium), such as silicon rubber or porous polypropylene, which allows the gas to diffuse into the medium without formation of bubbles. PA1 (3) Injecting air into the head space through outlets placed directly over the liquid surface. PA1 (4) Providing a revolving solid blade at the liquid surface for surface aeration.
The first two of these solutions suffer from severe disadvantages. Sparging produces foam; the permeable tube requires an excessive length of tubing which interferes with the circulation in the flask, and is difficult to clean. Injecting air requires more complex equipment, and the revolving solid blade achieves less than desireable oxygen transfer.